ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, August 30, 2024, 11:02 AM AKDT (Friday, August 30, 2024, 19:02 UTC)
No significant change occurred this week at Great Sitkin Volcano, where the ongoing effusive eruption continues to gradually fill the summit crater with lava. Satellite imagery from August 29 shows lava flow growth near the eruptive vent and trending northeast. Weakly elevated surface temperatures from the active lava flow surface were also observed when the weather was clear. Seismic activity was low and unchanged from previous weeks, with occasional small volcanic earthquakes.
The current, prolonged period of lava eruption at Great Sitkin Volcano began in July 2021 and has mainly been observed using satellite radar images that can view the volcano through cloud cover. A single explosive event occurred in May 2021; no other explosions have been detected since that time.
Great Sitkin Volcano is a basaltic andesite volcano that occupies most of the northern half of Great Sitkin Island, a member of the Andreanof Islands group in the central Aleutian Islands. It is located 26 miles (43 km) east of the community of Adak. The volcano is a composite structure consisting of an older dissected volcano and a younger parasitic cone with a ~1 mile (1.5 km)-diameter summit crater. A steep-sided lava dome, emplaced during the 1974 eruption, occupies the center of the crater. That eruption produced at least one ash cloud that likely exceeded an altitude of 25,000 ft (7.6 km) above sea level. A poorly documented eruption occurred in 1945, also producing a lava dome that was partially destroyed in the 1974 eruption. Within the past 280 years a large explosive eruption produced pyroclastic flows that partially filled the Glacier Creek valley on the southwest flank.
Earlier today, AVO lowered the Aviation Color Code to GREEN and the Volcano Alert Level to NORMAL at Shishaldin Volcano based on declining unrest. Slightly elevated seismicity, small infrasound signals and weak gas emissions continue to be detected but there is no indication of explosive activity or the presence of lava in the crater. This level of activity is expected to persist and continue to wane as the volcano settles after the eruption that began in July 2023 and continued until November 2023. The volcano appears to have returned to a background condition and poses no immediate threat of eruptive activity. Resumption of volcanic activity would likely be preceded by increased seismicity, infrasound, elevated temperatures, and gas emissions. Minor rock falls associated with collapse events from the unstable ground in and near the summit crater may generate small clouds of fine-grained dust that dissipate quickly near the summit.
Shishaldin Volcano is monitored by local seismic and infrasound sensors, web cameras, and a telemetered geodetic network. In addition to the local monitoring network, AVO uses nearby geophysical networks, regional infrasound and lighting data, and satellite images to monitor the volcano.
Shishaldin Volcano, located near the center of Unimak Island in the eastern Aleutian Islands, is a conical stratovolcano with a base diameter of approximately 10 miles (16 km). It is one of the most active volcanoes in the Aleutian volcanic arc, with at least 54 episodes of unrest including over 28 confirmed eruptions since 1824. Most eruptions are relatively small, although activity during July – November, 2023 generated ash columns that reached between 30,000 ft (9 km) and 42,000 ft (13 km) above sea level.
Matt Haney, Scientist-in-Charge, USGS mhaney@usgs.gov (907) 786-7497
David Fee, Coordinating Scientist, UAF dfee1@alaska.edu (907) 378-5460
The Alaska Volcano Observatory is a cooperative program of the U.S. Geological Survey, the University of Alaska Fairbanks Geophysical Institute, and the Alaska Division of Geological and Geophysical Surveys.